There are a now a number of free antivirus products on the market; many years ago it was just AVG but recently products like Avast! and Avira’s AntiVir
I always take online antivirus statistics with a pinch of salt, and I much prefer to go with personal experience. If you have the cash I’d recommend going with ESET NOD32 and also something like Prevx, I happen to be a reseller for both these products (Surprising that I’m recommending them then?) However if you don’t have or want to spend money, then I’d recommend going for Avira’s AntiVir. The only drawback to the free version of their product is the rather annoying popup adverts.
Check out the AV Comparatives tests at http://www.av-comparatives.org/comparativesreviews/main-tests
If you have any questions or concerns over security feel free to pay me a vist at http://www.atp-software.com and I'll be happy to arrange home visit of service on your IT equipment.